Portunatasaurus almost enters the LRT with dolichosaurs, not mosasaurs

Too few traits are present
for Portunatasaurus (Figs. 1–3) to be entered into the LRT without loss of resolution, but that shouldn’t stop us from figuring out what it is and what it isn’t.

Figure 1. Portunatasaurus compared to stem mosasaur, Aigialosaurus and to marine stem snake, Aphanizocnemus.

Figure 1. Portunatasaurus compared to stem mosasaur, Aigialosaurus and to marine stem snake, Aphanizocnemus.

From the Mekarski et al. 2019 abstract:
“A new genus and species of plesiopedal mosasauroid, Portunatasaurus krambergeri, from the Cenomanian–Turonian (Late Cretaceous) of Croatia is described.”

Ooops. Taxon exclusion rears its ugly head again. In the large reptile tree (LRT, 1823+ taxa) Portunatasaurus (Fig. 1) is closer to aquatic snake ancestors, like Aphanizocnemus (Fig. 1), than a “plesiopedal mosasaurid.” Even with so few traits to test, moving Portunatasaurus closer to mosasaurs and aigialosaurs adds 4 steps. In the LRT Aphanizocnemus nests as a snake ancestor: a marine varanoid dolichosaur scleroglossan squamate.

Figure 2. Portunatasaurus diagram with corrections.

Figure 2. Portunatasaurus diagram with corrections. Note the robust ribs, as in dolichosaurs. Mosasaurs and aigialosaurs have gracile ribs, a trait not tested in the LRT.

Mekarski et al. 2019 continue:
“An articulated skeleton, representing an animal roughly a meter long was found in 2008 on the island of Dugi Otok. The specimen is well represented from the anterior cervical series to the pelvis.”

There is no lumbar area in the Mekarsi et al. diagram (Fig. 2). Moving the pelvic area posteriorly to give Portunatasaurus a lumbar area agrees with other clade members. Note the robust ribs in Portunatasaurus, as in dolichosaurs. Mosasaurs and aigialosaurs (Fig. 1) have gracile ribs, a trait not tested in the LRT.

Figure 3. Portunatasaurus manus (right) and reconstructed with PILs (left).

Figure 3. Portunatasaurus manus (right) and reconstructed with PILs (left).

Mekarski et al. 2019 continue:
“Preserved elements include cervical and dorsal vertebrae, rib fragments, pelvic fragments, and an exquisitely preserved right forelimb. The taxon possesses plesiomorphic characters such as terrestrial limbs and an elongate body similar to that of basal mosasauroids such as Aigialosaurus or Komensaurus, but also shares derived characteristics with mosasaurine mosasaurids such as Mosasaurus.”

Note: the authors appear to have omitted dolichosaurs from consideration. Dolichosaurs are not mentioned in the abstract. Let me know if this is an error. I have contacted Mekarski for a PDF.

“The articulated hand exhibits a unique anatomy that appears to be transitional in form between the terrestrially capable aigialosaurs and fully aquatic mosasaurines, including 10 ossified carpal elements (as in aigialosaurs), intermediately reduced pro- and epipodials, and a broad, flattened first metacarpal (as in mosasaurines).

Note: the authors appear to be not looking at dolichosaurs. Whenever an author uses the word “unique” it is a good bet that pertinent taxa have been omitted because nothing in “unique” in evolution. What is unique for one clade is commonplace in another.

“The new and unique limb anatomy contributes to a revised scenario of mosasauroid paddle evolution, whereby the abbreviation of the forelimb and the hydrofoil shape of the paddle evolves either earlier in the mosasaur lineage than previously thought or more times than previously considered.”

Authors rarely consider the number one problem in paleontology: taxon exclusion. They prefer those headline-grabbing words like “unique” so they can postulate newer hypotheses ‘than previously considered.” Well, don’t we all… but these authors/PhDs are paid to do this and not make mistakes in taxon exclusion that an amateur with an online cladogram can pick apart without actually seeing the specimen.

“The presence of this new genus, the third and geologically youngest species of aigialosaur from Croatia, suggests an unrealized diversity and ecological importance of this family within the shallow, Late Cretaceous Tethys Sea.”

I assume it is a coincidence that mosasaur ancestors and unrelated snake ancestors were both found in the earliest Late Cretaceous strata surrounding today’s Mediterranean Sea. Let me know of Mekarski et al. tested dolicohosaurs in their cladogram. I had access only to the abstract and some figures.

The paper [PDF] just arrived.
No phylogenetic analysis is provided. Aphanizocnemus is not mentioned. Other dolichosaurs are compared.


References
Mekarski MC et al. 2019. Description of a new basal mosasauroid from the Late Cretaceous of Croatia, with comments on the evolution of the mosasauroid forelimb. Journal of Vertebrate Paleontology. 39: e1577872. doi:10.1080/02724634.2019.1577872.

wiki/Portunatasaurus

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